Powdering brush



7 May 2, 1933. F. T. POWERS 1,906,809

POWDERING BRUSH Filed May 1, 1931 INVENTOR Patented l t/lay 2, 1933 irltfi filtll FRANK 1. POWERS, F POUGLASTOIT, HEY V YORK POWDERING- BRUSHApplication filed May 1,

My invention relates to the art of making printing plates byphoto-mechanical processes, and more particularly to that step in theart in which the metal plate is prepared 5 by the application of resistto be acted upon by an etchant.

The object of my invention is to provide a powdering brush for use in amechanical powdering machine whereby resist in a powdered form may beapplied to the partially etched printing plate and a result attainedwhich is superior to results usually attained by expert hand operation.

In carrying out the process of making printing plates by what iscommonly called photo-engraving, it is now customary to perform each ofthe many steps involved by hand processes. The process as a whole is soWell understood and so generally practiced that a 2. detaileddescription is omitted herein and only that step described to which mypresent invention particularly relates, namely, the application of aresist in the form of a powder to the surface of the partially etchedplate.

This step is commonly called powdering and a plate is powdered four waysbetween each bite.

This application of resist is commonly accomplished by applying aquantity of powdered dragons blood to the surface of the plate and thenbrushing off the surplus with a broad flat brush usually made ofso-called camels hair. In brushing oil the surplus powder, it iscustomary to brush the plate in 3 but one direction during each of thefour powdering operations.

After each application and brushing of the powder, the plate is heatedto a temperature which melts or softens the powdered resist and causesit to adhere to and coat over those portions of the plate which it isdesired to protect against further etching. These portions which arenormally protected by the resist are the sides of the dots or lineswhich make up the design being etched, and it is the presence of thisprotection aii'orded by the resist that permits carrying the etchingprocess to suincient depth to give satisfactory printing quality. Themanner in which the powder is laid up against the sides of the SerialNo. 534,345.

dots and lines by the brushing process has a controlling influence onthe quality of the finished plate. Therein lies much of the skill of theetcher. Unless the powder is brushed against the lines and dots exactlyand uniformly the shoulders Will be ragged or undercutting will result.Either of these defects, i. e., ragged shoulders or undercutting, renderthe plate unsuitable for the production of mats for cylinder pressprinting for the to reason that the mats are caught in the raggedserrations of the shoulder or in the undercut ting, and can not beremoved from the plate Without serious injury. It is, therefore,particularly important that plates which are intended for newspaper andsimilar printing, where mats are used for preparing cast printing platesfor rotatory or cylinder presses, shall have smooth shoulders and befree from undercutting. 20

I find it possible to attain this desirable result universally anduniformly by substituting for the present common method of hand brushinga mechanical brushing device with a particular type of rotating brush. Iam aware that previous efforts have been made to apply powder to plateswith revolving mechanical brushes, but such efforts have not beensuccessful to such a degree as to displace hand brushing, largelybecause of the type of brush used. It requires a skilled etcher toperfectly powder a plate and the brushes which have been used heretoforein attempts to substitute revolving, power driven or manually operatedbrushes for the common hand brush, have not produced result-s comparablewith good, skilled, hand powdering.

I find that with my new type of brush in a powdering machine operatedeither by hand or from any suitable source of power, I can powder plateswith a degree of uniformity and perfection not attainable by even an eX-perienced etcher using a hand brush. And even the most inexperiencedoperator can produce perfect results with my brush.

in the accompan ing drawing the essential features of my invention areshown. Figure l is an isometric perspective view of one section of oneform of my new brush, of which Fig. 2 is an end View.

Figure 3 is a view of an assembled brush. Fig. 4 is an isometricperspective view of an alternate form. In Fig. 1 a cylindrical hub 1, ofsuitable material such as wood, sectors of which are studded with tuftsof fibrous material such as hair, 2, set in rows extendinglongitudinally along the outer surface of the cylinder leaving spaces orsectors, 3, on the surface of the cylinder, in which no tufts of fibrousmaterial are set.

In Fig. 2 I have shown more in detail the characteristics of my newbrush. A plurality of segments of the core are studded with tufts offibrous material. In Fig. 2 five such segments are shown marked a, b, 0,d and 6. Between these studded segments are an equal number of segmentsof the core in which no tufts of fibrous material are set. Thesesegments are marked f, g, h, 2' and j. Each segment of fibrous materialis trimmed off at its outer end at a bevel or taper such that the planep in which the outer ends of the fibrous material lies is at an angle Xof some 10 to 45 degrees with a plane tangent t to a circle 5 drawnabout the centre of the hub to circumscribe the outer tip ends of thesegments of fibrous material.

There are several methods used by brush makers in the manufacture ofcylindrical brushes. In Figs. 1 and 2, the method indicated is to anchorby means of wire 6 the tufts of fibrous material 2 into holes drilled inthe core. Vhen this method of manufacture is employed the length of thecylinder 1 is limited to the length which can be conveniently studdedwith tufts of fibrous material through the central opening in the corecylinder. I find this limit to be about four inches when the internaldiameter of the cylinder is about 1% inches. I, therefore, make up mybrushes of this type in sections about four inches long, and I use asufficient number of these sections placed end to end to make up a brushof any desired length.

In Fig. 3 a mandrel or shaft 8 of a diameter less than the internaldiameter of the cylinder shown in Fig. 1 has suitably mounted upon it aplurality of sections of brushes of the form showed in Fig. 1. Thesesections are held firmly in position upon the shaft by collars 9 whichare provided with set screws 10 by means of which they are held in placeon the sh aft. Screws 11 are provided in these collars by means of whichthe sections of brushes are clamped firmly in place and prevented frommovement relative to the shaft.

An alternate and also suitable method of construction of my new brush isshown in Fig. at, which illustrates a hollow cylindrical core equal tothe full length of the brush desired and set with tufts of fibrousmaterial 13 ccmented instead of wired into a multiplicity of holes inthe surface of the core without the use of wire and without drilling theholes completely through the shell of the core.

The characteristics of my new brush, which I find essential to itssuccessful operation and to the perfection of the results obtained arefirst the intermittent arrangement of the librous material around thecore of the brush; and second the trim or sectional contour of the outerend of each brush sector. The number of sectors of bristles andintervening blank spaces also has an influence upon the result, as doesalso the speed of rotation of the brush. As to the number of sectors, Ifind that there should be not less than three nor more than six, and Ifind that four or five sectors of bristles with, of course, an equalnumber of blank sectors intervening between the sectors of bristles, tobe the most satisfactory. As to the speed of rotation of the brush, Ifind that the optimum speed in revolutions per minute is such that thevelocity of travel of the periphery of the brush is between threehundred and six hundred feet per minute. As to the contours of the outerend of the brush sectors, I find that the beveled or chiseled formillustrated in Figs. 1 and 2 produces results having a degree ofperfection not attainable by other forms or cont-ours.

Having described my invention so that one skilled in the art may makeand use it, I now state what I believe to be new and novel, and forwhich I pray that Letters Patent be granted.

I claim:

1. A brush for the purpose set forth, having a plurality of sectors of acylindrical core set with tufts of fibrous material the fibres of whichare substantially radial to the center of the core, said sectorsalternating with sectors in which no tufts of fibrous material are set,and having the outer ends of said fibrous material substantially inimaginary planes forming acute angles with tangents to a circlecircumscribing the brush at the points of intersection of said imaginaryplanes and said circle, substantially as described.

2. A brush for the purpose set forth, having a plurality of sectors of acylindrical core set with tufts of fibrous material the fibres of whichare substantially radial to the center of the core, said sectorsalternating with sectors in which no tufts of fibrous material are set,and having the outer ends of said fibrous material substantially inimaginary planes forming angles of ten to forty-five degrees withtangents to a circle circumscribing the brush at the points ofintersection of said imaginary planes and said circle, substantially asdescribed.

3. A brush for the purpose set forth, comprising a cylindrical core onalternate sectors of the periphery of which are mounted tufts of fibrousmaterial, the fibres of which are substantially radial to the center ofthe core, to form a plurality of longitudinal strips of brush material,each strip having the outer ends of said fibrous material substantiallyin an imaginary plane, forming an acute angle With the tangent of acircle circumscribing the brush at the point of contact of the outermosttips of the fibres and a circumscribing circle, substantially asdescribed.

Signed at Douglaston, in the county 0i Queens, and State of New York,this 25th day of April, A. D. 1931.

FRANK T. POWERS.

